Prosthetic and orthotic devices for restoring or replacing lost lower-limb functions have been available for many years. Until recently, both types of devices were found as purely mechanical linkages making advantageous usage of simple mechanisms in order to preclude knee buckling in level walking stance phase, while still ensuring some form of swing motion during the aerial phase. While this type of device was shown to be fairly efficient in restoring the structural aspects of the lower-limb role in gait, their incapacity to properly sustain the wide variety of lower-limb dynamics associated with the various gait locomotion activities performed on a daily basis appeared as a sufficient limitation to sustain the development of more advanced devices.
While significant efforts were directed towards designing more advanced mechanisms allowing easier adjustment, or more progressive action, through pneumatics and hydraulics, the rapid advances in energy storage and computer technologies soon allowed to extend the realm of capacities associated with typical orthotic and prosthetic devices. Real-time configuration of passive braking devices such as disclosed, for example, in U.S. Pat. No. 5,383,939 and US Patent Application Publication No. 2006/0136072 A1, greatly improved the adaptability of prosthetic devices to user gait specificities or to variations of the environment in which the locomotion tasks are performed. Moreover, these prosthetic devices allowed the addressing of energy dissipative locomotion tasks in a physiologically-compliant manner never seen before. Although showing increased performance and dynamic adaptation with respect to the locomotion tasks being undertaken when compared to their predecessors, this first generation of computer-controlled prosthetic devices still lacked the adaptability and flexibility required to smoothly integrate into users' daily lives.
Integration of computer controls to the prosthetic and orthotic devices brought about changes to the control system in order to link sensory inputs to the dynamically configurable actuator. However, the purely dissipative nature of these devices greatly simplifies the problem as mechanical power exchanges between the user and the device are unidirectional (i.e., user has to initiate all tasks and provide mechanical power).
Latest efforts in the field of advanced orthotic and prosthetic devices, such as disclosed, for example, in US Patent Application Publication No. 2004/0181289 A1, partly resolved some of the limitations observed in the first generation of computer-controlled orthotic and prosthetic devices by providing a fully motorized prosthetic platform, allowing to address all major locomotion tasks, irrespective of their generative or dissipative nature. Requirements for computer-controlled system increased in complexity as the interactions between the user and the prosthetic or orthotic device were no longer solely initiated by the user. Through the use of a two layer control system, the motorized prosthetic or orthotic device allowed to efficiently manage the mechanical power exchange between the user and the device, such that the synergy between user and motorized prosthetic or orthotic device globally benefited the user. Adequate usage of the prosthetic or orthotic device capacity to generate mechanical power was observed to lead to increased gait quality and activity levels.
Nevertheless, the use of strict state machines to implement the artificial intelligence engine as the highest layer of the prosthetic or orthotic device control system is observed to impose a certain formalism on the manner in which the user executes typical locomotion tasks. While generating a certain learning burden on the user side, the use of firm triggers in order to trigger either distinct state transition or specific joint behavior greatly affects man-machine symbiosis. Moreover, limitations associated with the use of a strict state machine artificial intelligence engine when working in a highly variable environment (i.e., external environment and user himself) are well known and quickly show up as robustness issues from a system perspective. Finally, processing associated with the extraction of complex features associated with specific locomotion task detection is also known to generate a latency between measurement of the sensors value and implementation of the actual actions, which is often observed to greatly affect the prosthetic or orthotic device usability and performance.
Furthermore, common prosthetic or orthotic devices lack the ability to properly reproduce natural knee joint behavior and dynamic properties when used in a context that significantly differs from typical locomotion tasks. While generation of proper joint dynamics during cyclical locomotion portions ensure high symbiosis and user benefits, limitations observed in the capacity to reproduce natural joint compliance, or motions, in either non-locomotor or non-cyclical tasks significantly affect orthotic, or prosthetic, device usability and, accordingly, associated user benefits.